The present invention relates to a fuel cell, and more specifically to a fuel cell having an electrical circuit for shunting electrical power between the anode and cathode to improve the performance of the fuel cell and which further incorporates an energy storage device in combination with the electrical circuit which performs the shunting.
Fuel cells are well known in the art. A fuel cell is an electrochemical device which reacts a fuel and an oxidant to produce electricity and water. A typical fuel supply provided to a fuel cell is hydrogen, and a typical oxidant supply provided to a fuel cell is oxygen (or ambient air). Other fuels or oxidants can be employed depending upon the nature of the fuel cell and the design.
The basic process in a fuel cell is highly efficient, and for those fuel cells fueled directly by hydrogen, are substantially pollution free. Further, since fuel cells can be assembled into stacks of various sizes, fuel cell power systems have been developed to produce a wide variety of electrical power outputs, and thus can be employed in numerous commercial applications. As was discussed in our parent application, U.S. application Ser. No. 10/056,543, and which was filed Jan. 23, 2002 and which is incorporated by reference herein, the inventors disclosed a fuel cell having a controller which is electrically coupled to same, and which is configured to selectively electrically short the anode to the cathode of the fuel cell, and which further includes circuitry configured to measure the resistance of the fuel cell in timed relation to the electrical shorting. As disclosed in U.S. Pat. No. 6,096,449 the teachings of which are also incorporated by reference herein, a shunt and controller circuitry are disclosed and which periodically electrically shorts current between the anode and cathode of a fuel cell while simultaneously allowing the substantially continuous delivery of the fuel gas to the fuel cell. This periodic shunting has been shown to increase the overall electrical power output of the fuel cell. Still further, it is speculated that repeated and periodic electrical shorting causes each of the fuel cells to be xe2x80x9cconditioned,xe2x80x9d that is, such shorting is believed to cause an increase in the amount of water that is made available to the membrane electrode assembly (MEA) of the fuel cell thereby increasing the MEA performance by providing more uniform hydration. Still further, it is speculated that the electrical shorting provides a short term increase in heat dissipation that is sufficient to evaporate excess water from the diffuser layers which are often incorporated or made integral with the membrane electrode assemblies.
It is speculated that this evaporation of water caused by this periodic electrical shorting makes more oxygen from the ambient air available to the cathode side of the membrane electrode assembly. Whatever the ultimate cause, the electrical shorting appears to increase proton conductivity of the membrane electrode assembly. This increase in proton conductivity results in a momentary increase in the electrical power output of the fuel cell which diminishes slowly over time. The overall increase in the electrical power output of the fuel cell, as controlled by the adjustably sequential and periodic electrical shorting of individual and groups of fuel cells, results in an increase in the overall electrical power production of the entire serially connected group of fuel cells.
While the above discussed arrangements, and schemes have worked with a large degree of success, one noted shortcoming apparent in their design is that the electrical power that is shunted between the anode and cathode is largely lost during the shunting interval. Therefore, it would be advantageous to provide a fuel cell which provides the benefits provided by the prior art teachings, but which avoids the perceived shortcomings individually associated therewith. These and other aspects of the present invention will be discussed in greater detail below.
A first aspect of the present invention is to provide a fuel cell having an anode and a cathode and which produces a voltage output which is supplied to a load; an electrical energy storage device; and a controller electrically coupled to the fuel cell and which periodically shunts the voltage output of the fuel cell between the anode and cathode by electrically coupling the electrical energy storage device to the anode and the cathode of the fuel cell.
Still another aspect of the present invention relates to a fuel cell having an anode and a cathode, and which produces an electrical current having a voltage output and which is delivered to a load, and which includes an electrical energy storage device which is selectively electrically coupled to the fuel cell, and which is further selectively electrically coupled to the load; and a controller for selectively delivering the voltage output of the fuel cell to the load, and periodically shunting the voltage output between the anode and cathode by selectively electrically coupling the electrical energy storage device to the anode and cathode, and wherein the voltage output of the fuel cell during the shunting is stored as an electrical charge by the electrical energy storage device, and wherein the electrical energy storage device is selectively discharged to deliver the stored electrical charge to the load.
Still another aspect of the present invention relates to a fuel cell having an anode and a cathode, and which produces an electrical power output which is delivered to a load, and which includes first electrical circuitry which selectively electrically couples a fuel cell having a voltage and electrical current output to a load; an output bus which is electrically coupled with each of the first electrical circuitry and with the load; second electrical circuitry which is electrically coupled to the first electrical circuitry, and wherein the first electrical circuitry shunts the electrical current and voltage output of the fuel cell between the anode and cathode thereof; a controller electrically coupled in controlling relation relative to the first and second electrical circuitry, and in voltage and electric current sensing relation relative to the electrical output of the fuel cell, and the voltage and current demand of the load; and an electrical energy storage device which is selectively electrically coupled with the second electrical circuitry and which stores the voltage and electric current output of the fuel cell when the first electrical circuitry shunts the voltage and electric current output of the fuel cell between the anode and cathode thereof, and wherein the electrical energy storage device is selectively electrically discharged by the second electrical circuitry to deliver the stored voltage and electric current output to the load.
These and other aspects will be discussed in greater detail below.